1. Field of the Invention
The present invention relates to novel regulatory elements which confer tapetum-specificity to gene expression. In particular, this invention is directed to a tapetum-specific regulatory element of the maize SGB6 gene, and to using such a regulatory element to produce transgenic, male-sterile plants. Moreover, this invention is directed to a method for restoring male fertility in the progeny of male-sterile plants.
2. Background
Control of pollen fertility is essential in hybrid crop production. In hybrid maize production, control of pollen fertility is typically accomplished by physically removing the male inflorescence, or tassel, prior to pollen shed. Manual detasseling is highly labor intensive. Although mechanical detasseling is less labor intensive than manual detasseling, mechanical detasseling is less reliable and requires subsequent examination of the crop and possibly, remedial manual detasseling. Both methods of detasseling cause a loss of yield.
Pollen fertility also can be controlled by applying a chemical composition to the plant or soil to prevent pollen production in female plants. See, for example, Ackmann et al., U.S. Pat. No. 4,801,326. According to this method, hybrid seeds are produced by the cross fertilization of the treated female plants with pollen from non-treated plants. However, the chemical approach is labor intensive, and presents potential problems with the toxicity of chemicals introduced into the environment.
Another approach to the control of fertility is based upon the use of a cytoplasmic gene(s) for male sterility. See, for example, Patterson, U.S. Pat. No. 3,861,079. The problem with this approach, however, is that the expression of certain cytoplasmic male sterility genes is accompanied by increased susceptibility to fungal pathogens. For example, extensive use of one cytotype, cmsT, led to an epiphytic outbreak of Southern Corn Leaf Blight in the early 1970's. Although additional cms cytotypes have become available, their use has not become widespread due to the concern over possible susceptibility to the Southern Corn Leaf Blight pathogen, or to other, as yet unknownpathogens.
A need therefore exists for a method to control pollen production without reliance on naturally occurring male sterility genes or, the traditional manual, mechanical, and chemical methods.